Source measure units (SMU) are used to make precision measurements in many fields, including the testing of semiconductor products. For example, U.S. Pat. No. 5,039,934 describes one such device and range-changing in such a device is described in U.S. Pat. No. 5,144,154, both of which are incorporated herein by reference in their entireties. Source measure units force either a voltage or a current and then respectively measure a resulting current or voltage. SMUs may operate in source or sink mode. Internal power dissipation is equal to the output current multiplied by the difference in the internal voltage supply and the output voltage. Because sinkmode current is returned to the opposite voltage supply rail internally, the internal power dissipation in sinkmode is twice the maximum internal power dissipation in sourcemode. For this reason, output stage amplifiers and cooling are commonly designed for the worst-case (sinkmode) power dissipation. This usually results in over-designed cooling for the majority of users since sinkmode is typically used less often than sourcemode. Sometimes thermal monitoring is performed in the background, which is slow to respond and not necessarily robust. It is desirable to provide improved techniques for monitoring the safe operating areas of an SMU in both source and sinkmode operation.